WO2025159520A1 - Coil for wireless charging and wearable device including same - Google Patents

Abstract

A coil for wireless charging and a wearable device including same are disclosed. The coil for wireless charging, according to an aspect of the present invention, is made by winding a Litz wire, wherein the Litz wire comprises a plurality of strands, the plurality of strands each have a diameter or maximum width of 0.02-0.05 mm, and the number of the plurality of strands is 23-144.

Description

Wireless charging coil and wearable device including the same

The present invention relates to a wireless charging coil and a wearable device including the same.

Recently, efforts have been continuously made to increase the wireless charging power of wearable devices. Due to their small size, implementing wireless charging in wearable devices can be challenging due to the difficulty in configuring large wireless charging antennas. Consequently, wearable devices inevitably supply lower power than smartphones, resulting in longer charging times.

Additionally, in the case of wearable devices, the alignment between the wireless charging transmitter and the wireless charging receiver installed in the wearable device is often poor, and the resulting loss often results in longer wireless charging times.

Therefore, research is also being conducted on RF wireless charging, which has a higher degree of freedom in charging compared to the existing magnetic induction method, so that wireless charging can be performed smoothly even if the alignment of the wireless charging transmitter and receiver devices is somewhat misaligned.

In this case, technology is being reviewed to increase the wireless charging power from 1 to 2 W, which is low compared to the existing magnetic induction wireless charging, to 5 W, by increasing the charging frequency from the existing 100 kHz band to 1.78 MHz or higher.

One RF-based wireless charging technology is the AirFuel Alliance standard magnetic resonance wireless charging. This technology efficiently transfers energy through the same resonant frequency between the transmitting and receiving coils, operating primarily at 6.78MHz (the AirFuel Resonant standard). This method utilizes the resonant frequency to provide high efficiency over medium distances (tens of centimeters to 1 meter) and can be used in smart devices, medical devices, and IoT devices.

However, due to the nature of wearable devices, the size of the wireless charging antenna is small, which limits the ability to increase charging power. In addition, as the frequency increases, the skin effect occurs, concentrating the current on the surface of the conductor, reducing the effective cross-sectional area and rapidly increasing the coil resistance. This causes heat generation and reduced charging efficiency. For example, if a conventional solid wire is used as a wireless charging coil, there is a problem in that the resistance rapidly increases from 0.4Ω to over 2.0Ω as the operating frequency increases.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a wireless charging coil configured to reduce coil resistance and heat generation and improve charging efficiency at an operating frequency of a high frequency band exceeding 100 kHz, particularly at an operating frequency of 1.78 MHz, and a wearable device including the same.

The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description below.

According to one aspect of the present invention, a wireless charging coil is provided that is made by winding a Litz wire, wherein the Litz wire includes a plurality of fine strands, each of the plurality of fine strands has a diameter or maximum width of 0.02 mm or more and 0.05 mm or less, and the number of the plurality of fine strands is 23 or more and 144 or less.

At this time, the wireless charging coil can operate at an operating frequency in the range of 1 MHz or more and 2 MHz or less.

At this time, the wireless charging coil can operate at an operating frequency of 1.78 MHz.

Meanwhile, the plurality of thin lines can be formed to have the same cross-section.

Meanwhile, the plurality of fine lines may be formed such that any one of the plurality of fine lines has a different cross-section from the other.

Meanwhile, each of the plurality of wires may include a core made of a conductor.

At this time, each of the plurality of fine wires may further include an insulating layer coated on the outer surface of the core material.

At this time, each of the plurality of fine wires may further include a heat-sealing coating layer coated on the outer surface of the insulating layer.

Meanwhile, the cross-section of each of the plurality of lines may have either a circular or polygonal shape.

Meanwhile, the above Ritz wire can be formed by winding it 10 to 30 times in one layer.

Meanwhile, the above Ritz wire can be formed by dividing it into two layers and winding each layer 5 to 15 times.

According to another aspect of the present invention, a wearable device including the wireless charging coil can be provided.

According to the above configuration, a wireless charging coil according to one aspect of the present invention is made by winding a Litz wire composed of a plurality of fine wires, wherein each of the plurality of fine wires constituting the Litz wire has a diameter or maximum width of 0.02 mm to 0.05 mm, thereby reducing the skin effect in an operating frequency band exceeding 100 kHz, preferably an operating frequency band of 1 MHz to 2 MHz, and more preferably an operating frequency of 1.78 MHz, thereby alleviating the current density imbalance on the surface of a conductor and reducing electrical loss. Through this, energy loss occurring during a wireless charging process can be minimized and charging efficiency can be improved.

Furthermore, by mitigating the proximity effect caused by magnetic field interactions between adjacent conductors in high-frequency environments, energy loss can be reduced and coil efficiency can be improved. This technology can also reduce heat generation due to reduced electrical loss, enhance system thermal stability, and ensure consistency in transmission distance and output performance.

Additionally, the structural flexibility and diverse design options of Ritz wire enable optimized coil design, maximizing the transmission efficiency and performance of wireless charging systems.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the composition of the invention described in the claims.

FIG. 1 is a drawing showing a wireless charging coil according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a Ritz wire constituting a wireless charging coil according to one embodiment of the present invention.

Figure 3 is a cross-sectional view of the fine wires constituting the Ritz wire illustrated in Figure 2.

FIG. 4 is a diagram showing the results of a resistance test for a wireless charging coil according to one embodiment of the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein. To clearly explain the present invention, parts irrelevant to the description are omitted in the drawings, and the same reference numerals designate identical or similar components throughout the specification.

The words and terms used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of the present invention, in accordance with the principles by which the inventor can define terms and concepts in order to best explain his or her invention.

Therefore, the embodiments described in this specification and the configurations illustrated in the drawings correspond to a preferred embodiment of the present invention, and do not represent all of the technical ideas of the present invention, so there may be various equivalents and modified examples that can replace the configuration at the time of filing of the present invention.

In this specification, terms such as “include” or “have” are intended to describe the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

When a component is said to be "in front of," "behind," "above," or "below" another component, this includes not only being placed "in front of," "behind," "above," or "below" the other component in direct contact with it, but also if there is another component intervening therebetween. Furthermore, when a component is said to be "connected" to another component, this includes not only being directly connected to one another, but also being indirectly connected to one another, unless there are special circumstances.

FIG. 1 is a drawing showing a wireless charging coil according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of a Litz wire constituting a wireless charging coil according to one embodiment of the present invention, and FIG. 3 is a cross-sectional view of a thin wire constituting the Litz wire illustrated in FIG. 2.

For reference, in Fig. 2, only one of the multiple thin wires (110) constituting the Ritz wire (100) is indicated with a drawing symbol.

Referring to FIGS. 1 to 3, the wireless charging coil (10) according to the present embodiment is made by winding a Ritz wire (100).

The wireless charging coil (10) may be used as an antenna mounted on a wearable device to wirelessly receive power, or as an antenna mounted on a wireless charger to wirelessly transmit power. In other words, the wireless charging coil (10) may be used as a part of a wireless charging transmitter or as a part of a wireless charging receiver.

The wireless charging coil (10) can be used for RF wireless charging.

The Litz wire (100) includes a plurality of fine wires (110). The plurality of fine wires (110) are combined in a form of being twisted in a spiral manner or arranged in parallel adjacent to each other to form the Litz wire (100).

A plurality of thin lines (110) can be connected in a mutually external form.

When a wireless charging coil (10) is made by winding a Ritz wire (100) including a plurality of fine wires (110), the skin effect is reduced and heat generation is reduced compared to when a wireless charging coil is made by winding a general wire composed of a single strand.

According to one embodiment of the present invention, each wire (110) may include a core material (111), an insulating layer (112), and a heat-sealing coating layer (113).

The core (111) can be made of a metal with high electrical conductivity, such as copper. The core (111) can have a predetermined length and a circular cross-section.

An insulating layer (112) may be coated on the outer surface of the core material (111). The insulating layer (112) may be formed of a known insulating material.

A heat-sealing coating layer (113) is formed on the outer surface of the insulating layer (112). The heat-sealing coating layer (113) can be formed of a known heat-sealing material such as varnish.

When heat is applied to a plurality of fine wires (110) in a spirally twisted state, a portion of the heat-sealing coating layer (113) of each fine wire (110) melts and hardens, thereby bonding the plurality of fine wires (110) to each other. In this case, the plurality of fine wires (110) can be easily and simply bonded by the heat-sealing method.

Alternatively, although not shown, each wire may include a core and an insulating layer, excluding a heat-sealing coating layer. In this case, a plurality of wires may be helically twisted and integrally bonded to each other using a known adhesive method.

Alternatively, although not shown, each wire may include a core and an insulating layer, excluding a heat-sealing coating layer. In this case, the multiple wires may be integrally joined to each other by a finishing layer surrounding the multiple wires. For example, the finishing layer may be made of a known heat-sealing material.

In this case, when the Litz wire is wound into a coil shape and heat is applied, the finishing layer melts, and the plurality of fine wires arranged within the finishing layer can be joined to each other by the melted and hardened finishing layer. The plurality of fine wires (110) constituting the Litz wire (100) can be arranged in a form of mutual external contact.

Alternatively, although not shown, the plurality of wires that make up the Litz wire may each contain only a core made of a conductor such as copper.

According to one embodiment of the present invention, the cross-section of each of the plurality of fine wires (110) may be circular. In this case, the cross-section of the Litz wire (100) formed by the plurality of mutually contiguous fine wires (110) may have a structure in which a partially empty space is formed. In this case, the cross-section of the Litz wire (100) may have an overall circular or nearly circular shape.

At this time, it is preferable that the height or thickness of the cross-section of the Litz wire (100) does not exceed 0.2 mm overall. If the height or thickness of the cross-section of the Litz wire (100) exceeds 0.2 mm, the overall thickness of the coil becomes thicker, and the thickness of the wireless charging transmitter or wireless charging receiver including the coil becomes thicker, making it difficult to apply it to a wearable device with a narrow installation space.

Alternatively, although not shown, the cross-section of each of the plurality of thin lines may be a polygon, such as a triangle, a square, or a pentagon. For example, if the cross-section of each thin line is a regular polygon, the plurality of thin lines may be arranged so that no empty space is created between the circumscribed thin lines.

At this time, the cross-section of the Litz wire including multiple fine lines may be a polygon such as a triangle or a square. At this time, it is preferable that the height of the cross-section of the Litz wire, or in other words, the thickness, does not exceed 0.2 mm.

In one embodiment of the present invention, a plurality of thin lines (110) can be formed to have the same cross-section as in FIG. 2.

Alternatively, although not shown, the plurality of thin lines may be formed such that one of the thin lines has a cross-section different from the other thin lines. Here, a different cross-section means that at least one of the cross-section shapes or areas is different.

In one embodiment of the present invention, the cross-section of the fine wire (110) is circular. At this time, the diameter of each fine wire (110) constituting the Ritz wire (100) is formed to satisfy a set range. Here, the set range may be 0.02 mm or more and 0.05 mm or less.

If the diameter of the fine wire (110) is less than 0.02 mm, the cost of producing the fine wire (110) increases rapidly because the diameter of the fine wire (110) is too small, and if the diameter of the fine wire (110) exceeds 0.05 mm, heat generation increases rapidly in an operating frequency band exceeding 100 kHz, specifically in an operating frequency band of 1 MHz or more and 2 MHz or less, and more specifically in an operating frequency of 1.78 MHz.

Meanwhile, in another embodiment of the present invention, although not shown, if the cross-section of the thin line is a polygon other than a triangle, the maximum width of the thin line may be 0.02 mm or more and 0.05 mm or less. Here, the maximum width means the longest length between two points where the cross-section of the thin line and any straight line intersect.

For example, if the cross-section of a thin line is a square or a rectangle, the maximum width is the length between two non-adjacent vertices. In other words, if the cross-section of a thin line is a square or a rectangle, the maximum width is the length of the diagonal.

As another embodiment of the present invention, although not shown, if the cross-section of the thin wire is triangular, the maximum width of the thin wire may be 0.02 mm or more and 0.05 mm or less. Here, the maximum width refers to the length of the longest side among the three sides of the triangle. Fig. 4 is a diagram showing the results of a resistance test on a wireless charging coil according to one embodiment of the present invention.

In Fig. 4, the experimental example (Case 2) is a wireless charging coil wound with Litz wire, including 45 fine wires, each having a diameter of 0.035 mm. The experimental example (Case 2) corresponds to an example of a wireless charging coil according to the embodiment described above.

In Fig. 4, the control example (Case 1) is a wireless charging coil wound with a Litz wire including 16 fine wires, each fine wire having a diameter of 0.06 mm.

In the experiment on Fig. 4, the cross-sectional area of the Litz wire of the experimental example (Case 2) and the cross-sectional area of the Litz wire of the control example (Case 1) have similar sizes.

Specifically, in the control example (Case 1), the cross-sectional area of 16 thin wires with a diameter of 0.06 mm is 0.0452 mm², and in the experimental example (Case 2), the cross-sectional area of 45 thin wires with a diameter of 0.035 mm is approximately 0.0433 mm², so the cross-sectional areas of the Litz wires of the control example (Case 1) and the experimental example (Case 2) are similar.

However, since the cross-sectional area of 16 strands of 0.06 mm thin wires is 0.0452 mm², which is 0.00194 mm² larger than the approximately 0.0433 mm² of 45 strands of 0.035 mm thin wires, the control example (Case 1) can have lower resistance and higher current capacity than the experimental example (Case 2).

However, when the operating frequency is in the high frequency range, for example, the 1.78 MHz band, and when the skin effect and proximity effect are considered in addition to the resistance and current capacity of the conductor, it can be confirmed through the graph in Fig. 4 that the experimental example (Case 2) is more advantageous in terms of electrical characteristics and high-efficiency design.

Referring to Fig. 4, it can be seen that there is no significant difference between the control example (Case 1) and the experimental example (Case 2) in the low-frequency band around 100 kHz, but the resistance of the control example (Case 1) increases rapidly as the operating frequency increases.

This is because, in high-frequency currents, the current flows only on the surface of the conductor due to the skin effect, so if the diameter of the conductor is large, the inside is hardly used and the current flows only on the surface, reducing the effective cross-sectional area.

Therefore, compared to the control example (Case 1), the experimental example (Case 2) composed of fine wires with a small diameter has a relatively low resistance due to an increase in the effective cross-sectional area of each fine wire, which increases the path through which current can flow, thereby increasing the high-frequency current transmission efficiency.

Furthermore, in the high-frequency region, the proximity effect occurs, where the current distribution between adjacent conductors is distorted by the magnetic field generated as current flows along the conductor. In this case, an experimental example (Case 2) consisting of multiple strands of small-diameter wires can insulate each wire, thereby reducing the proximity effect and minimizing energy loss.

The experimental results as in Fig. 4 can be applied when the diameter of each fine wire constituting a Litz wire satisfies the set range, that is, 0.02 mm or more and 0.05 mm or less, and the cross-sectional area of a Litz wire is formed similarly to the cross-sectional area of the Litz wire of the control example (Case 1).

For example, if the diameter of the fine wires constituting a certain Litz wire is 0.02 mm, the certain Litz wire requires 144 fine wires in order for the cross-sectional area of the certain Litz wire to be equal to or similar to the cross-sectional area of 0.0452 mm² of the Litz wire of the control example (Case 1) of FIG. 4.

In this way, even when the diameter of the fine wires constituting the Litz wire is 0.02 mm and the number of fine wires is 144, the resistance of this Litz wire can be significantly reduced compared to the Litz wire of the control example (Case 1) of Fig. 4 for the same reason as described above.

As another example, when the diameter of the fine wires constituting a Litz wire is formed to be 0.05 mm, similar to the control example (Case 1) of Fig. 4, 23 fine wires are required to have a cross-sectional area similar to the cross-sectional area of the Litz wire of the control example (Case 1) of Fig. 4.

In this way, when the diameter of the fine wires constituting the Litz wire is 0.05 mm and the number of fine wires is 23, the resistance of this Litz wire can be reduced compared to the Litz wire of the control example (Case 1) of Fig. 4.

Referring to the examples above, when the diameter of the fine wires constituting the Litz wire is within a set range, that is, 0.02 mm or more and 0.05 mm or less, the number of fine wires constituting the Litz wire may be 23 or more and 144 or less in order to have a cross-sectional area similar to the control example (Case 1) of Fig. 4.

In this way, when the diameter of the fine wires constituting the Litz wire is 0.02 mm or more and 0.05 mm or less, and the number of fine wires is 23 or more and 144 or less, the resistance of the Litz wire may be smaller than that of the Litz wire of the control example (Case 1) of Fig. 4.

Meanwhile, a wireless charging coil according to one embodiment of the present invention can be configured by applying 10 to 30 coil turns of a Ritz wire as illustrated in FIG. 1. At this time, the coil turns can be applied entirely to one layer, but if the area of the wireless charging coil allowed for the wearable device to which it is applied is narrow, it is also possible to configure it by dividing it into two layers and applying 5 to 15 turns to each layer.

That is, the number of turns and layers of the coil affect the inductance, and in a two-layer configuration, the number of turns is distributed among each layer, so if the total number of turns is the same, the inductance value can remain the same or similar.

However, when the coil is configured with one layer, the magnetic field combination is maintained at a constant level because each turn is uniformly distributed on the plane, but when the coil is configured with two layers, a gap is created between the layers, but since the magnetic fields in each layer overlap, a magnetic field coupling efficiency similar to that of the single layer can be maintained.

In particular, if the operating frequency is fixed to 1.78 MHz as in the present invention, the inductance of the coil and the resonance value of the capacitor are adjusted according to the design, so that the same power transmission is possible even in a two-layer configuration by matching the resonance frequency.

Meanwhile, when configured in two layers, the length of the coils increases, which may create a gap between the coils, which may increase resistance and lead to power loss. Therefore, it is necessary to use a wireless charging coil with excellent high-frequency efficiency, such as a Litz wire as in the present invention.

In addition, if the configuration is made of two layers, there is a concern that the magnetic field may be dispersed, which may reduce the magnetic field coupling efficiency. To prevent this, the spacing and alignment of the Litz wires of each layer must be performed consistently, and even if the number of turns is reduced through the two-layer configuration, it is possible to maintain the intended power efficiency by adjusting the capacitance through the coil design to match the same resonance conditions as the one-layer configuration.

The wireless charging coil (10) described above can be installed in wearable devices such as smart watches, smart rings, AR (Augmented Reality), VR (Virtual Reality), and XR (Extended Reality) devices and used as a receiving antenna for wireless charging.

This wireless charging coil (10) has a Litz wire (100) including a plurality of fine wires (110), and each of the plurality of fine wires (110) has a diameter or maximum width of 0.02 mm or more and 0.05 mm or less, so that it has a remarkably low electric resistance characteristic in an operating frequency band exceeding 100 kHz, preferably in an operating frequency band of 1 MHz or more and 2 MHz or less, and more preferably in an operating frequency of 1.78 MHz, thereby remarkably reducing heat generation and having high charging efficiency.

Although the embodiments of the present invention have been described, the spirit of the present invention is not limited to the embodiments presented in this specification, and those skilled in the art who understand the spirit of the present invention will be able to easily propose other embodiments by adding, changing, deleting, or adding components within the scope of the same spirit, but this will also be considered to fall within the spirit of the present invention.

Claims (12)

A wireless charging coil made by winding Ritz wire. The above Ritz wire comprises a plurality of fine wires, The diameter or maximum width of each of the above plurality of fine lines is 0.02 mm or more and 0.05 mm or less, A wireless charging coil, wherein the number of the plurality of wires is 23 or more and 144 or less. In the first paragraph, The above wireless charging coil is a wireless charging coil that operates at an operating frequency in the range of 1 MHz or more and 2 MHz or less. In the second paragraph, The above wireless charging coil is a wireless charging coil that operates at an operating frequency of 1.78 MHz. In the first paragraph, A wireless charging coil, wherein the plurality of wires are formed to have the same cross-section. In the first paragraph, The above multiple lines are, A wireless charging coil, wherein one of the plurality of wires is formed to have a different cross-section from the other. In the first paragraph, Each of the above multiple lines, A wireless charging coil comprising a core made of a conductor. In paragraph 6, Each of the above multiple lines, A wireless charging coil further comprising an insulating layer coated on the outer surface of the core material. In paragraph 7, Each of the above multiple lines A wireless charging coil further comprising a heat-sealing coating layer coated on the outer surface of the insulating layer. In the first paragraph, A wireless charging coil, wherein each cross-section of the plurality of wires has a shape of either a circle or a polygon. In the first paragraph, A wireless charging coil formed by winding the above Ritz wire 10 to 30 times in one layer. In the first paragraph, A wireless charging coil formed by dividing the above Ritz wire into two layers and winding each layer 5 to 15 times. A wearable device comprising a wireless charging coil according to any one of claims 1 to 11.